Most Mandarin syllables have multiple meanings, so whenever the American ecologist Robbie Hart greets strangers in China, he explains the meaning behind Du, his Chinese name.

“Du as in cuckoo flower,” he says, referring to du juan hua, the Mandarin term for rhododendron.

In 2009, Mr. Hart began traveling to China’s Yunnan Province to study rhododendrons, a flowering plant with famously pretty flowers. About half the world’s roughly 1,000 rhododendron species are native to Yunnan and areas of Nepal, Bhutan, and Myanmar (Burma) – a region that was a favorite destination of 19th and early 20th century American and European explorers who traveled east at the urging of Western botanical curators and green-thumbed aristocrats.

Hart, a graduate student at the Missouri Botanical Garden and the University of Missouri, St. Louis, has inspected more than 10,000 of the explorers’ archived flowers at museums and institutions across Europe and the United States. He is now comparing them with his present-day rhododendron samples. But unlike his footloose predecessors, his aim is to see whether rhododendron behavior during the past century reflects changing global weather patterns.

He is one of a small handful of botanists in the world who study climate change by analyzing how flowering plants are adapting their flowering cycles in response to warming global temperatures. Botanists say such research is important because it draws on little-known historical data to help illuminate the scientific present.

“When these collections were established, no one really thought about climate change research,” says Richard Primack, a professor of biology at Boston University who studies flowering plants in the US and several Asian countries. But today they help scientists “to very consistently demonstrate that climate change is the new reality.”

Chronicle of flowers

It's rewarding to study plant collections in regions where botanists have made a habit of roaming. Mr. Primack, for example, inspects naturalist records that writer Henry David Thoreau kept of Concord, Mass. Scientists Yasuyuki Aono and Keiko Kazui analyze 9th century chronicles of flowering cherry trees in Kyoto, Japan.

Yunnan Province, which is close to the size of California, is a particularly fascinating place to study flowering plants because its dense jungles and soaring mountain ranges are jewels of biodiversity. According to Sun Hang, deputy director of the Kunming Institute of Botany, Yunnan’s climate ranges from tropical to arctic, and although it covers just 4 percent of China’s total land area, it contains more than half of the country’s 16,200 documented plant species.

Western plant hunters began flocking to Yunnan en masse in the late 19th century. They typically shipped their flower specimens by ship from Chinese ports to European and American museums or herbariums, or to wealthy Western gardening enthusiasts eager to decorate their lavish estates with flowering exotics.

Now Hart, the fourth-year University of Missouri graduate student, is traveling to Cambridge, Edinburgh, and other cities to photograph flower specimens that Mr. Rock collected in Yunnan’s Himalayan foothills. In China, Hart creates spreadsheets of Rock’s data on his laptop and hikes the Himalayas in search of the flowering rhododendrons that his predecessor collected nearly a century ago.

Responding to climate change

How are Yunnan’s rhododendrons responding to climate change? "It gets to be a pretty complicated question,” Hart says on a recent field trip to Yuhu. “But it does look like they are being pushed up the mountain."

Hart, who conducts research in China thanks to roughly $120,000 in grants from the National Science Foundation, says it can be difficult to accurately compare withered flower specimens with living plants. And although he is grateful for the logistical support he receives from the Kunming Institute of Botany, he says, he also struggles to access official scientific data and navigate China’s complex science bureaucracy.

But Hart does have access to villagers from the local Naxi ethnic group. Many of them are keenly aware of rhododendron flowering cycles, and their general impression is that flowering patterns are growing increasingly erratic – an observation that complements Hart’s emerging data sets.

The villagers, though, don’t confirm that rhododendrons are moving higher up in the Himalayas in search of cooler temperatures, as his data suggest. Hart says that is largely because such changes happen over centuries rather than decades, and partly because some villagers don’t know what to make of his scientific inquiries.

“What are you talking about?” they reply when Hart asks if their rhododendron bushes are traversing mountainsides. “Trees can’t walk!”